Workers evacuated after gas levels rise - incident at Metropolitan Colliery 21 March 2019

1. David Gordon – Inspector of Mines Coal
Safety and Health Representatives Seminar September 2019
Workers Evacuated After Gas Levels Rise
Metropolitan Colliery – 21st March 2019

3. • 6:00pm the issue began with the longwall face stopped on high CO2 in return.
• 7:15pm withdrawal of all underground persons begins. Withdrawal TARP activated
rising CH4 levels.
• 8:45pm all persons underground withdrawn to the surface and accounted for.
• LW return recorded CH4 to 16.1%, CO2 to 15.9% and O2 to 13.5% in 43m3/s.
• Main upcast shaft recorded CH4 to 3.01%, CO2 to 4.16% in 280m3/s.
• Workforce out of the mine for seven days.
• 2.9 million cubic metres of gas released in 6 days. 38% CH4 and 62% CO2.
Facts

4. Gas trends – LW return tube bundle

5. Gas trends – LW return real time

6. Gas trends – Upcast shaft tube bundle

7. Gas trends – Ellicott diagram LW return

8. Gas trends – Ellicott diagram upcast shaft

9. Where did the gas come from?

10. Where did the gas come from?

11. • Most likely source appears to be from surrounding strata below the working seam.
• Limited data available for the mining area.
• Gas assumed to be released by a combination of factors
• Fracture profile around the LW
• Change in depth of cover
• Mining through a syncline
• Loading event on the supports
• No identified geological structure in the immediate area
• No cross measure drainage holes due to lack of identified geological structure
• Tube bundle gas monitoring continued to function
• Real time gas monitoring very limited
Findings

12. 1. Managing the gas reservoirs around extraction panels:
a. Ensure there is enough reliable exploration data available to determine the
geotechnical risks and gas reservoir affected by the proposed mining method.
b. Include a means to determine which reservoir the gas is released from to
confirm design and modelling assumptions.
c. Include lithology above as well as below the intended working seam.
d. Consider significant gas capture with the gas drainage process and have
minimal contamination of accessible mine airways.
Recommendations – focusing on

13. 2. Withdrawal trigger action response plans (TARPs):
a. Design TARPs to reflect realistic triggers and actions that are simple to
follow.
b. Develop a process to ensure the workforce are aware and understand the
TARPs in use at the mine.
3. Use of self-contained self-rescuers:
a. Consider expanding the training on self-rescuers to include use during times
where low oxygen environments are encountered and excessive levels of
carbon-dioxide gas.
b. Develop TARPs in relation to the circumstances when self-rescuers are
expected to be used.
Recommendations – focusing on

14. 4. Post incident monitoring:
a. Mines should conduct a risk assessment to determine atmospheric
monitoring requirements post incident (explosion, fire, gas event, etc.). This
should include both real time and tube bundle.
b. The selection of post incident monitoring arrangements should consider the
post incident survivability of the system and system elements.
c. Post incident monitoring arrangements should operate effectively when
power is removed from all or parts of the mine.
d. Post incident monitoring points should be installed in optimal locations such
as intake airways, return airways and escape routes.
e. Monitoring for gases relevant to the incident should form part of the post
incident monitoring arrangements. This should ensure the concentration range
of the gases being monitored are appropriate.
f. Implement a program of testing the effectiveness of the post incident
monitoring arrangements.
Recommendations – focusing on

15. 5. Re-entry procedures:
a. Mines should conduct a risk assessment to determine re-entry conditions
appropriate for the various risks identified.
b. Develop TARPs to reflect acceptable and unacceptable conditions.
6. Workers’ access to return airways during extraction activities:
a. Mines should conduct a risk assessment to determine the controls necessary for
workers to safely access return airways.
b. Develop a procedure to reflect those controls identified.
c. Consider the timing of access, barometric change effects, production activities,
whether working alone is appropriate, remote workings, communications and gas
detection.
d. Review requirements for appropriate gas monitoring, communications and
emergency escape for those workers accessing return airways in the event a
withdrawal is required.
Recommendations – focusing on

16. 7. The determination of acceptable methane levels passing through the ventilation
fans:
a. Mines should conduct a risk assessment to determine the maximum levels
of methane that will be allowed to pass through the main ventilation fans.
b. Develop TARPs to guide workers at the mine in the decision-making
process when excessive quantities of various gases are being exhausted from
the mine.
c. Explore options to be able to conduct simple ventilation changes remotely
from the surface to manage unexpected gas issues underground.
d. Explore options to be able to remotely limit the volumes of methane gas
levels that pass through the fan infrastructure.
Recommendations – focusing on

17. 8. Management of ventilation fan exhaust gases around surface infrastructure:
a. Mines should conduct plume modelling in relation to the main surface
ventilation fans.
b. Conduct hazardous area assessments to include relevant infrastructure that
may be affected by these exhaust gases.
9. Review site emergency management and withdrawal procedures:
a. Include accurate monitoring of the locations of workers and man transport
vehicles to facilitate timely and efficient withdrawal.
b. Include the availability of man transports in work areas.
Recommendations – focusing on

18. David Gordon
david.gordon@planning.nsw.gov.au
Thank you.
Questions?